Magnetic tilt compensated heading compass with adaptive zoffset

• US 7,826,999 B1
• Filed: 09/18/2007
• Issued: 11/02/2010
• Est. Priority Date: 08/20/2007
• Status: Expired due to Fees

• Current Assignee: PNI Corporation (PNI Digital Media)
• Original Assignee: PNI Corporation (PNI Digital Media)
• Inventors: Boeen, Anders, Taylor, Andrew T., Figaro, Davy J.
• Primary Examiner(s): Wachsman; Hal D
• Application Number:
  US11/856,973
• Time in Patent Office: 1,141 Days
• Field of Search: 702/141, 702/85, 702/92
• US Class Current: 702/141
• CPC Class Codes: G01C 17/02 Magnetic compasses
• CPC Class Codes: G01C 25/005 initial alignment, calibration or starting-up of inertial devices

Abstract

The instant invention utilizes two, optionally orthogonal and optionally slightly tilted, horizontal magnetic sensors and, optionally, a 2 or 3 axis accelerometer or inclinometer to calculate a pitch, roll and tilt compensated heading. A vertical, Z, component is relatively constant compared to X and Y components, the Z component can be abstracted from the X and Y sensor when pitch and roll is applied based on Z offset measured with X or Y sensor at high tilt angles. Additional sensors tilted at various θ degrees can be added with a different angle α to X sensors when additional horizontal and magnetic coverage is desirable.

Claims

1. A magnetic tilt compensated heading compass comprising:

a means for communicating with a means for calculating a tilt compensated heading;

a first and second magnetic field sensor for acquiring magnetic field data aligned with respect to each other at an included angle β

; and

a first and second accelerometer for acquiring tilt compensation data and aligned such that the first and second accelerometer are operable with the first and second magnetic field sensors;

wherein the magnetic tilt compensated heading compass communicates magnetic field and tilt compensation data to a means for calculating a tilt compensated heading operable to calculate a heading such that the tilt compensated [Heading] equals ATAN2{Y″

/X″

} wherein X″

is the tilt compensated magnetic field vector in the X direction in the earth frame of reference and Y″

is the tilt compensated magnetic field vector in the Y direction in the earth frame of reference and wherein at least one of said first and second magnetic field sensors has a tilt in a ±

Z axis direction of angle θ

wherein 2≦

θ

≦

88 degrees, absolute.

2. A magnetic tilt compensated heading compass of claim 1 wherein said means for calculating is operable to determine a NewZoffset(n) such that:

NewZoffset(n)=Zoffset(n)*WeightingNew+Zoffset(n−

1)*WeightingOld

wherein Zoffset(n) contains the current first and second magnetic field sensor data and Zoffset (n−

1) contains the just previous first and second magnetic field sensor data.

3. A magnetic tilt compensated heading compass comprising:

a first magnetic field sensor wherein the first magnetic field sensor is tilted in a ±

Z axis direction of angle θ

such that 2≦

θ

≦

88 degrees, absolute;

second magnetic field sensor aligned with respect to the first magnetic field sensor at an included angle β

; and

a means for calculating a tilt compensated heading from data acquired by the first and second magnetic field sensors wherein the tilt compensated heading comprises a Zxoffset and a Zyoffset wherein

Zxoffset=X*WeightingNew+Zxoffset*WeightingOld

Zyoffset=Y*WeightingNew+Zyoffset*WeightingOld

WeightingNew is the weight of the new value in an adaptive forget algorithm;

WeightingOld is the weight of the old value in an adaptive forget algorithm;

X is the compass orientation of magnetic component in X direction;

Y is the compass orientation of magnetic component in Y direction;

Zxoffset is the magnetic component in Z direction with pitch near 90 degrees measured by the first magnetic field sensor; and

Zyoffset is the magnetic component in Z direction with roll near 90 degrees measured by the second magnetic field sensor.

4. A magnetic tilt compensated heading compass of claim 3 wherein said means for calculating a tilt compensated heading is remote from said first and second magnetic field sensors.

5. A magnetic tilt compensated heading compass comprising:

a first magnetic field sensor tilted in a ±

Z axis direction of angle θ

such that 2≦

θ

≦

88 degrees, absolute;

a second magnetic field sensor aligned with respect to the first magnetic field sensor at an included angle β

;

wherein the first and second magnetic field sensors acquire magnetic field data; and

a means for calculating a tilt compensated heading employing a Zoffset and data from the first and second magnetic field sensors such that the tilt compensated [Heading] equals A TAN 2{Y″

/X″

} wherein X″

is the tilt compensated magnetic field vector in the X direction in the earth frame of reference and Y″

is the tilt compensated magnetic field vector in the Y direction in the earth frame of reference.

6. The magnetic tilt compensated heading compass of claim 5 further comprising a Zoffset with forget function.